Voltage multiplier circuit



April 19, 1949. 5 HARR|5 2,467,744

VOLTAGE MULTIPLIER CIRCUIT Filed Aug. 1, 1947 FIG. I

0.0. 1 6 r cm SOURCE FIG. 2

AC. SOURCE JNVENTOR.

SAMUEL J HARRIS BY X XM ATTORNEY Patented Apr. 19, 1949 UNITED. STATES PATENT OFFICE VOLTAGE MULTIPLIER CIRCUIT Samuel J. Harris, Fort Wayne, Ind., assignor, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application August 1, 1947, Serial No. 765,338

3 Claims. 1

This invention relates to transformerless power supplies and particularly to a circuit for multiplying the voltage developed by a source of unidirectional or alternating voltage.

It is conventional practice to provide a rectifier circuit'arranged to double the peak voltage developed by an alternating voltage source. It has also been proposed to provide a circuit including a plurality of diodes and condensers arranged in cascade for repeatedly multiplying the voltage of an alternating voltage source. However, a circuit of this type has the drawback that a large number of diodes and condensers'i's required to obtain an output voltage that is appreciably higher than the input voltage.

In a television receiver, for example, a unidirectional voltage of the order of several thousand volts is required for accelerating the cathode ray of the television image reproducing tube. Thus, for a television receiver a voltage multiplier would be desirable for multiplying the unidirectional anode voltage of the receiver which usually amounts to about 300 volts only thereby to develop a unidirectional voltage of the order of several thousand volts required for the image reproducing cathode ray tube.

It is an object of the present invention, therefore, to provide a novel voltage multiplier circuit which requires a minimum of components.

A further object of the invention is to provide a simple voltage multiplier circuit which permits to multiply the voltage of a. unidirectional or alternating voltage source by a large factor.

In accordance with the present invention, there is provided a voltage multiplier circuit comprising a source of voltage. There are provided a first electric storage element such as a condenser variable between a maximum and a minimum capacitance and means for varying the capacitance of the first condenser. There is further provided a second electric storage element which may also be a condenser. Finally unilaterally conducting means are provided for coupling the source of voltage to the two condensers to charge the first condenser from the voltage source when the capacitance of the first condenser is near its maximum value and to discharge the first condenser into the second condenser when the capacitance of the first condenser is near its minimum value. In this manner a voltage is developed across the second condenser which is higher than the voltage of the voltage source. Actually. the output voltage is multiplied by a factor which equals the ratio of the maximum 2 to the minimum capacitance of the first condenser.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a circuit diagram of a voltage multiplier connected to a direct current source and embodying the present invention, while Fig. 2 is a circuit diagram of a modified voltage multiplier in accordance with the invention connected to an alternating current source.

Referring now to Fig. 1, there is illustrated a voltage multiplier comprising direct current source I having two output terminals 2 and 3, output terminal 3 being connected to ground as illustrated. Source I may develop a positive unidirectional voltage with respect to ground. Two unilaterally conducting devices 4 and 5 are connected in series to output terminal 2 of source I and may, for example, consist of diodes as illustrated. Variable condenser E connects the junction point of diodes l and 5 to ground, that is to terminal 3, while fixed condenser l connects the output electrode of diode 5, that is, its cathode to ground.

In accordance with the present invention, variable condenser 6 may be a rotatable condenser which may, for example, be driven through a motor 8 by means of a driving connection indi-- cated at l0, A filter network, which may include series coil II and shunt condenser [2, may be coupled to condenser I for smoothing out the voltage derived from the voltage multiplier,

The voltage multiplier circuit of Fig. 1 operates as follows. Let it be assumed that, initially, condensers 6, l and I2 are discharged. As soon as source I is connected to the circuit, diodes 4 and 5 will become conducting and the condensers will charge upto the voltage developed across terminals 2 and 3. Let it be further assumed that the capacitance of variable condenser 6 alternately is increased and decreased to a maximum or minimum value by means of motor 8. It is well known that the voltage V of a condenser depends upon its charge Q and its capacitance C as follows: =Q/C. Accordingly, as the capacitance of condenser 6 decreases, its voltage increases and vice versa.

When the voltage across condenser 6 thus increases, due to a decrease of its capacitance, the cathode of diode 4 will become positive with respect to its anode, and consequently, current con- .multiple of that across terminals 2 and 3. The

factor by which the input voltage is multiplied depends upon the ratio of the maximum capacitance of condenser 6 to its minimum capacitance. This ratio could be made as high as 20 to 1 so that, if the voltage across terminals 2 and 3 amounts to 300 volts, the voltage across condenser I will eventually increase to 6,000 volts. Since diodes 4 and i only conduct when the capacitance of rotatable condenser 6 is near its maximum or minimum value, the capacitance of condenser 6 need not vary continuousiy,' but might abruptly change from a maximum to a minimum value.

The voltage multiplier circuit of the present invention may with advantage be used in a color television receiver where condenser 6 may be driven by the motor that rotates the color wheel of the receiver.

Referring now to Fig. 2, in which like components are designated by the same reference numerals as were used in Fig. 1, there is illustrated a modified voltage multiplier which includes an alternating current source lli having output terminals 2 and 3. Diodes 4 and I are again connected in series to terminal 2 of voltage source I 5. The junction point of diodes 4 and is connected to ground through variable condenser IS. The output electrode of diode I, that is, its cathode is connected through choke coil I! to shunt condenser l8. Coil l1 and condenser l8 form part of a filter network which further includes series choke coil 20 and shunt condenser 2|.

Variable condenser I6 is preferably of the vibratory type. The capacitance of condenser l6 may be varied between a maximum and a minimum value by means of an electromagnet 22 energized by winding 23 which preferably is connected to alternating current source I! as shown. Electromagnet 22 accordingly will vibrate its armature 24 to which is connected one of the plates of variable condenser 16.

The capacitance of condenser I6 is accordingly varied in synchronism with the frequency of the alternating voltage of source is impressed on diodes 4 and 5. The capacitance of condenser l8 should have its maximum value when the alternating input voltage has a positive peak and, therefore, the capacitance will have a minimum when the alternating input voltage has its negative peak.

The circuit of Fig. 2, therefore, operates in substantially the same manner as that of Fig. 1. During the positive peak of the input voltage, diode 4 will become conducting to charge variable condenser Hi. When the capacitance of condenser It has reached its minimum, diode 5 will become conducting to charge condenser II. It is preferred to charge condenser is through a choke coil such as I! which may form part of the filter network. Since diode 4 only conducts when the voltage of source if has a positive peak, it is to be understood that the voltage multiplier circuit of the present invention will also operate if source ll develops positive pulses instead of a sinusoidal wave. The voltage multiplier of the present invention requires a minimum of component elements and at the same time it is able to multiply the input voltage by a large factor.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and. it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A voltage multiplier circuit comprising a source of a voltage wave, a first condenser variable between a maximum and a minimum capacitance. means for varying the capacitance of said first condenser in synchronism with the frequency of said wave, a second condenser, and unilaterally conducting means for coupling said source to said condensers to charge said first condenser from said source when the capacitance of said first condenser is near said maximum capacitance and to discharge said first condenser into said second condenser when the capacitance of said first condenser is near said minimum capacitance, thereby to develop a voltage across said second condenser that is higher than the peak voltage of said wave.

2. A voltage multiplier circuit comprising a source of alternating voltage having two output terminals, two unilaterally conducting devices connected in series to one of said terminals and having an output electrode, a first electric storage element connected between the junction point of said devices and the other one of said terminals. means for periodically varying the capacitance of said first element in synchronism with the frequency of said alternating voltage, and a second electric storage element connected between said output electrode and the other one of said terminals, thereby to develop a voltage across said second element that is higher than that across said terminals.

3. A voltage multiplier circuit comprising a source of alternating voltage having two output terminals, two diodes connected in series to one of said terminals and having an output electrode, a first condenser connected between the junction point of said diodes and the other one of said terminals, means for periodically varying the capacitance of said first condenser in synchronism with the frequency of said alternating voltage so that said capacitance is at a maximum when said alternating voltage has a peak, a second condenser connected between said output electrode and the other one of said terminals, and a filter network coupled to said second condenser, thereby to develop a voltage across said second condenser that is higher than that across said terminals.

SAMUEL J. HARRIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,694,966 Clinker Dec. 11, 1928 2,413,391 Usselman Dec. 31, 1946 2,417,452 Stiefel Mar. 18, 1947 2,418,128 Labin et al Apr. 1, 1947 

